Gluconic acid aqueous solution as a sustainable and recyclable promoting medium for organic reactions

For the first time, gluconic acid aqueous solution (GAAS), a biobased weakly acidic liquid, was used as an effective promoting medium for organic reactions, such as the Michael addition of indoles to alpha,beta-unsaturated ketones, the electrophilic ring-opening reaction of 3,4-dihydropyran with indoles and Friedel-Crafts alkylation of electron-rich aromatics with benzyl alcohols. The concept of using GAAS as a solvent for organic reactions not only offers a sustainable candidate for progress in solvent innovation, but also opens up a new avenue for the utilization of this biobased polyhydroxylated acid. Among the features that render GAAS as a solvent so interesting is the ability to act as both the reaction medium and catalyst. Moreover, this methodology offers significant improvements with regard to the yield of products, simplicity in operation, cost efficiency and green aspects, in terms of avoiding toxic catalysts and minimizing the generation of waste.